The Court of Justice has issued a press release summarizing the procedure nicely. You can find it here. It sets out the three features that distinguish it from the normal preliminary reference procedure:
"In the first place, with the aim of speeding up the process, the urgent preliminary ruling procedure makes a distinction between the persons who may participate in the written stage of the procedure and those entitled to participate in the oral stage. In the new procedure, only the parties to the main proceedings, the Member State of the court making the reference, the European Commission and, if appropriate, the Council and the European Parliament (if one of their measures is at issue) are authorised to lodge written observations in the language of the case within a short period of time. The other interested persons and, in particular, the Member States other than that of the referring court, do not have that opportunity but are invited to a hearing at which they may, if they wish, submit their oral observations on the questions referred by the national court and on the written observations lodged.
In the second place, the internal handling of cases under the new procedure is accelerated considerably, as all cases falling within the area of freedom, security and justice are, as soon as they reach the Court, referred to a Chamber of five judges specifically designated for a period of one year to be responsible for the screening and processing of such cases. If that Chamber decides to allow a request for the urgent procedure to be applied, it will go on to give its ruling shortly after the hearing, and after hearing the Advocate General.
Finally, to ensure the desired expeditiousness, the procedure will, in practice, essentially be conducted electronically. Communication between the Court and the national courts, the parties to the main proceedings, the Member States and the Community institutions will, as far as possible, be electronic."
The Court has also issued a new supplemental information note on the urgent procedure addressed to national courts on how it will operate.